Chapter 5- The standard indications for the application of one-piece, T-type
and two-piece types
Director of Kuroyama Oral and Maxillofacial Surgery Clinic
Yushiro Kuroyama
I.

The difference between one-stage and two-stage types

The numbers of stages indicate the number of surgical steps involved. The installation of one-stage type iscomplete with one surgical intervention, whereas two stages, for first the burial of the fixture, and second
the fenestration surgery are required for the two-stage type.
Generally, the values of each method have been concluded that the treatment period can be reduced withthe one-stage type, while the two-stage type has been noted of its high success rate. Along with the others,
their pros and cons are listed in Table 2-5-1. The notably high success rate of two-stage type is largely beowing to the burial of the fixture under the mucoperiosteum for several months without any exertion ofpressure, enabling firm integration with the bone. Due to the higher risk of infection with the one-stage
type than with the two-stage type, its application has been limited in cases where the bone is insufficientin terms of its width and height, and where bone augmentation procedure is necessary.
Nevertheless, concomitant installation of one-piece type with GBR membrane to conduct immediateloading has always been a success from my experience (Fig.2-5-2). From such observations, I have come toquestion the conditions indicated for the two-stage and one-stage types, as they have not always been
appropriate.
In the past, besides the disadvantages of the two-stage type such as the added complications in theprocedure such as the increased number of surgical steps, lengthened treatment period, the costcompared to the one-stage type, as well as loosening of the screws or fracture problems had been
identified and reported. In the development of the AQB two-stage type, these issues were solved byrenovating the screw systems.
One-stage type
Advantage: - Can complete the procedure in one go.
Disadvantage: - Occlusal force, labial force and buccal force can all be exerted from theearly stages
Two-stage type-The epithelial downgrowth can result early in the course of healing.

Advantage: - Easier to obtain primary stability with this method
Disadvantage: - Fenestration procedure is required-

The gap in between the fixture and abutment-

Loosening of the screws and fracture-

Loosening of the abutment

Fig. 2-5-1 Properties of one-stage and two-stage types

Fig. 2-5-2 a to g An example of immediate loading with the one-piece type implant
Under the standard implant treatment, roughly 4 months is required to allow the healing process of theextraction cavity before the installation of implants. The bone healing on the buccal side was thought tooccur in its resorbed state, therefore was treated as stated below:
a. Bone defect was observed in the buccal side of No.21, where immediate loading was conducted.
b. , c. Hole punching in the absorbable membrane with a circular knife, and the hole that matches
the diameter of the implant.
d. Filling with PRP and -TCP.
e. Radiograph taken directly after the surgery.
f.

Radiograph after 4 months after the surgery.

g. Radiograph after 3 years and ten months from the surgery.
II. Properties of AQB implant system
The one-piece, one-piece one-stage T-type, two-piece one-stage and two-piece two-stage are included in the
product lineup of the AQB implant system (Fig.2-5-3) and are all possible to be applied. When the AQB
implant was first placed on the market, only one-piece type was present. The effectiveness of one-stage
method and HA coating had both been rejected by the world, and thus had to face severe views in thesales. But 15 years since the start of its sales, with the technique in which to convert the -TCP coating2)
into recrystallized HA with hydrothermal treatment, 3),4) one-piece one-stage has proved its efficacy withthe clinical trial results, and good longevity.

a. One-piece typeb. One piece T-typec. Two-piece one staged. Two-piece two stage(one stage)
Fig. 2-5-3 Basics of AQB implant system
Recently, various studies on examining the safety of implants were conducted, and the general
understanding of the one-stage type became one that said, provided that a suitable treatment isconducted with the one-stage type, there are no significant differences in the infection risk with thetwo-stage type. For example, in a study that observed the one-stage and two-stage type titanium implant
5 years from the implantation with X-ray radiography, there was no difference in the survival rate
between the two.5) In addition, from the animal studies I conducted in Tokyo Medical and Dental
University, as shown in Fig 2-5-4, 2-5-5, the comparison of bone resorption between the two types with
the X-ray radiography (at initial stage, a month, 3 months and 5 months after the implantation), showedno significant difference.
Of course if there are concerns as to the efficacy and the clinical results of one-stage type, two-stage typecan be applied to all of the cases. The survey to the AQB users (n=228) conducted in 2001 by ADVANCE
Co., Ltd. indicated 83% of the users to demand inclusion of two-piece type in the AQB Implant system(Fig.2-5-6-a). The reasons for this were for cases where angled orientation was required, for esthetic
outcome, for edentulous jaw, application as a support for the denture, and to apply immediate loading(Fig.2-5-6-b).

Fig. 2-5-4-a,b Experiment on German Shepherd. Recrystallized HA coated (50 μm) implant sample wasinstalled 3 months after the tooth extraction.

One stage

Two stagea. Right after the implantation b. One month later c. Three months laterd. Five months later

Fig. 2-5-5 Radiograph images of one-stage and two-stage implants installed (Experiments were
performed in Tokyo Medical and Dental University). No significant bone resorption could be observedwith one-stage type even after 5 months from its implantation.

Fig. 2-5-6 A survey conducted to find out the need for two-piece type implant (ADVANCE Co., Ltd., 2001,
n = 228).
In the development of the two-piece type, AQB team investigated the means to improve the accuracy ofinterdigitation in order to overcome the issues faced with the two-piece type that were circulating at thetime such as the loosening of the screws and fracture. The result of this research led to the idea ofinternal joint to connect the fixture and the abutment (Fig. 2-5-7) with titanium alloy (Ti-6Al-4V) screw.
The interlocking part of the fixture and the abutment takes a SOL (smooth octagonal lock) interdigitation
system that disperses the stress applied (Fig.2-5-8). The interdigitation has been structured with
precision machining technology and its high precision is evident from the SEM image (Fig.2-5-9).
The thorough investigation resulted in the release of AQB two-piece type implant that incorporated theadvantages of one-piece type, to widen the cases that the AQB implants can be applied to. A clear
standard for selecting the one-piece or two-piece types does not exist, but for many of the users of AQB
implant system, the first-line choice is the one-piece one-stage type as is the main product of this system,
can be applicable to most of the cases; and two-piece for the more complex cases.6) The operation of thetwo-piece type can be conducted with the addition of SOL driver bit, a Hex driver bit and a torque control(Fig. 2-5-10) to the conventional tools for one-piece type.

Fig. 2-5-8 SOL system (smooth octagonal lock system)Fig. 2-5-7 AQB two-piece system

The octagonal interdigitation without the acutecorners can evenly disperse the stress exerted.

Eight different interdigitations can be selected.

Fig. 2-5-9 SEM image of theFig. 2-5-10

interdigitation of the two-piece typea) SOL driver bitb) HEX driver bitc) Torque control

In 2007, AQB one-piece T-type that has been added with a 6º inclination angle to the abutment was also
introduced into the system (Fig. 2-5-11-a). The tapered structure was suited to prevent the subsidence
and aberration of the implant structure into the maxillary sinus after socket-lift or sinus-lift procedures.
Its abutment diameter is 0.4 mm thicker than that of the one-piece type therefore the tooth cervix of thesuperstructure was able to be designed to be thicker. The only time a tool specific for T-type is required isfor its implantation with a fixer (Fig. 2-5-11-b).
To investigate the strength of the implant neck of AQB one-piece, two-piece and T-type, a bending
strength test was conducted with stroke speed 0.5 mm/s applied with weight (N) (Fig. 2-5-12). The
bending strength was the in the order: one-piece < two-piece < T-type (Fig. 2-4-13, y-axis show the relative
bending strength to the strength of the one-piece 3 mm diameter implant to be set as 1).
The result that the bending strength of the one-piece type to be weaker than that of two-piece type was
unexpected, but the reason for this can be largely owed to the titanium alloy (Ti-6Al-4V) screw and to the
SOL interdigitation system (Fig. 2-5-8). The increase in the abutment diameter with T-type was due tothe shift in the positioning of the screw, this can be said to be the reason for the higher relative strength of
the T-type to the one-piece type (Fig. 2-5-14,15).7)

Fig. 2-5-11-a,b One piece T type (a) and a specific fixer for T type (b)<Bending strength test>

Stroke speed

Load (N)M3 screw

Fig. 2-5-12 Strength comparison of implant neckFig. 2-5-13 The result of the bending strength test

Coating boundary

Screw boundary

Fig. 2-5-14 Comparison of the screw sections of
one-piece type and one-piece T-type

Screw parts got bigger as a result of formation of screw
abutment in transition

Fig. 2-5-15
The reason for the increase in the strength of the
one-piece T-type is that the increased strength is dueto the repositioning of the portion of the screw.

III. Selection criteria for maximizing the properties of one-piece, two-piece and T-types
A. One-stage (one-piece, two-piece)
The simple structure of the one-piece one-stage type can be applied to most of the cases. The use of
two-piece one-stage type to particular cases in which the inclined angle, parallel nature are required andbe completed at once (Fig. 2-5-16). Alternatively, there are cases where two-stage method initiallyintended to become treated as for a one-stage method due to the exposure of the healing abutment (Fig.
2-5-17) during the consolidation stages. This is not considered as an issue provided that bone integration
can be established.
B. Two-stage (two-piece)
Two-stage two-pieces are often applied in situations where achieving bone integration is considered to beof prime importance, and where infection and loading need to be avoided. It is also effective where
inclined angle on the abutment of to adjust the parallel nature of the multiple installed implants are
required (Fig. 2-5-18 to 20).
Fig. 2-5-16 Case examples of one-stage:
one-piece and two-piece types
a. One-piece type: preparation of abutment
teeth
b. One-piece type: superstructure placementc. Two-piece type: postoperative placement ofhealing abutment to await its consolidationd. Two-piece type: superstructure placement

Fig. 2-5-17 Healing cap becoming exposed.
Sinus-lift procedure was conductedsimultaneously with the implantation to theleft maxillary molars. The healing abutment of
the No. 2 position became uncovered.
a. Radiograph with the exposure of healing
abutmentb. Image of the oral cavity

Fig. 2-5-18 A case of multiple
implantation

withtwo-piece

two-stage typea. Abutment placementb. Superstructure placement

Fig. 2-5-19 A case in which an inclined angle and parallel nature of the abutment was modified with
two-piece two-stage typea. Panoramic radiograph with the multi-abutment placementb. Placing the abutment that have been adjusted to be in parallel with the adjacent structuresc. Placement of superstructure

Fig. 2-5-20 A case in which angling was provided
with the two-piece two-stage typea. Preoperative image of the oral cavity
b. Panoramic radiograph after the primary
operationc. Fenestration procedured. Dental radiograph after the placement of
abutment (the degree of angle adjustment at
No. 11 position was more than what was
expected)
C. T-typee. Placement of superstructure

T-type is suited to prevent the subsidence and aberration of the implant structure into the maxillarysinus after socket-lift (Fig. 2-5-21) or sinus-lift procedures, as well as for immediate loading following
tooth extraction (Fig.2-5-22). Previously, one-piece type was the main type installed when associated withsocket-lift or nasal sinus floor elevation (Fig. 2-5-23). Recently, however, to such examples with low bonedensity, and narrow bone, it has become more common for the two-stage type or T-type to be applied (asshown in the example featured in Fig. 2-5-17-a, the implant subsiding into the maxillary sinus interior

has been prevented with the use of diameter 4 mm fixture and 5 mm diameter healing abutment SS to
the positions No. 3 and 4).
Each one-piece, two-piece and T-types in conjunction with sinus-lift (simultaneously) have been shown in
Fig. 2-5-24. All of the examples show favorable outcome, but T-type seems to show convenience in terms of
preventing implant body from subsiding. The advantage of T-type is in its ability to stop sliding into themaxillary sinus especially where the cancellous bone is particularly soft. Implantation is conducted byobserving the coating layer therefore the implants can be inserted further than was initially planned
especially with the soft bone.

Fig. 2-5-21 A case of T-type socket-lift
a. Intra-oral image (2 months postoperatively)
b. Dental radiograph straight after the operation (no bone filling agents are used)c. Dental X-ray 4 months after the operation (osteogenesis of the maxilla can be seen, by theosteoconductive property of HA.

Fig. 2-5-22 A case of T-type immediate loading after tooth extraction. The distance to the mandibular
canal is relatively short, therefore applied T-type to prevent the subsiding of the implant and for a better
fit at the cervix to the funnel-shaped extraction socket
a. The remaining root was extracted to be replaced with T-type implant (5 mm diameter, 10 mm inlength of the HA coated section).
b. The image of the oral cavity a month after operationc. The image of the oral cavity two months after operationd. Preoperative radiograph to No. 30
e. Postoperative radiograph 2 months and 2 weeks later (2 weeks after the superstructure placement).

Fig. 2-5-23 A case of sinus-lift with T-type implant, immediately after the tooth extraction, with elevationof the floor of nasal sinus. The sinus-lift was conducted with β-TCP and PRP.
a. Preoperative image of the oral cavity
b. Preoperative panoramic radiographc. Perioperative image during the extraction of the anterior tooth and sinus-lift procedure to the leftd. CT image of the region to which sinus-lift was conducted (thickness of the cortical bone: approx 2
mm).
e. Image of the oral cavity after the implantationf.

Postoperative panoramic radiographg. Image of the oral cavity after sinus-lift procedure to the right, and during extraction of right maxillarycanineh. Panoramic radiograph featuring the dental arch, 11/2 years after the placement of the superstructure.
No problems have been encountered thus far.
i.

Image of the dental arch, 11/2 years after the placement of the superstructure. No problems have beenencountered thus far.

Fig. 2-5-24 Sinus-lift conducted in conjunction with each typeof AQB implants. One-piece type implants were inserted to
the No. 2, 4, 5 positions (No. 2 is not included in the image).
Judging from the buccal bone quantity directly from thelateral window, the cortical bone of the maxillary sinus floor
appears relatively thick. However, it was confirmed to bethin as 1.5 mm with the CT scan, therefore the implant body
could not be stabilized with the bone if inserted in parallel. In
order to prevent the subsidence into the maxillary sinus,
implant body had to be stabilized so that it was in a slanted
position.
a., b. Image and radiograph of the oral cavity post-operation
with one-piece typec., d. Image and radiograph of the oral cavity post-operation
with T-typee., f. Image and radiograph of the oral cavity post-operation
with two-piece type
D. Comparison of the types in designing their margins
The main factor of concern in terms of the esthetics of one-stage and two-stage types is their emergenceprofile. As shown in Fig. 2-5-25, the edge of the superstructure of one-piece one-stage type is often placed
close to or on top of the gingival margin therefore giving a base of the superstructure that spreads to thesides. On the contrary, the superstructure margin can be placed beneath the gingival margin with thetwo-piece type thus providing a natural emergence profile.
This is still possible with the one-piece type, but as it requires a number of tedious steps such as incising
into the gingival structures surrounding the abutment, pressurize the area with provisional crown andwait for it heal, the application of two-stage type is recommended from the beginning.

Fig. 2-5-25 The gingival margin and the positioningof the superstructures of one-piece and two-piecetypes
a. Gingival margin of one-piece typeb. Gingival margin of two-piece typec. Superstructure positioning with one-piece typed. Superstructure positioning with two-piece type

Fig. 2-5-26 Incision into the gingiva for one-stage
typea. After the incision of the gingiva surrounding theimplant
b. Healing of the gingiva surrounding implant (2weeks later)
Examples using each of the different types were presented in this chapter, but the first-line choice,personally, is with the one-piece one-stage type, and apply the T-type and two-stage types accordingly tothe conditions presented (Table 2-5-1, 2) although, it is indeed possible to select and apply T-type or
two-piece type only to all of the cases presented.
1. Elevation surgery (Socket lift, maxillary sinus floor augmentation procedure, and nasal cavity
elevation etc)
2. Immediate implant insertion right after tooth extraction
3. Case of attach greater importance to strength
Table 2-5-1 Cases where use of T-type is recommended
1. Case which angulation is necessary① Depend on bone conditions of front tooth maxilla and implant part② Occlusal condition such as shift between opposing teeth space and interalveolar crest line
③Necessity of parallelism for multiple teeth
2. Case of postoperative early infection and wants to avoid early overload
3. Case of low bone density
4. Case which attaches put greater importance on esthetics (Emergence profile)
5. Case of edentulous jaw (Full maxillary prosthetics)
Table 2-5-2 Cases where use of two-piece two-stage type is recommended
1. Angling is required① In the anterior region or due to the bone structure of the implanting region② For correcting occlusion- to fit the opposing teeth, or shift relative to the interalveolar crestline③ Implantation in parallel to the adjacent structures is required with cases of multiple implantinstallation.
2. Infection, or loading directly after the operation needs to be prevented
3. Low bone density
4. Esthetics (a good emergence profile) is required
5. Edentulous jaw
6. Recovery from the perioperative loosening with one-stage type implantReferences
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